Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
Data is typically written to the disk by modulating a write current in an inductive coil (write coil) to record magnetic transitions onto the disk surface in a process referred to as saturation recording. During read-back, the magnetic transitions are sensed by a read element (e.g., a magneto-resistive element) and the resulting read signal demodulated by a suitable read channel. Heat assisted magnetic recording (HAMR) is a recent development that improves the quality of written data by heating the disk surface during write operations in order to decrease the coercivity of the magnetic medium, thereby enabling the magnetic field generated by the write coil to more readily magnetize the disk surface. Any suitable technique may be employed to heat the surface of the disk in HAMR recording, such as by fabricating a laser diode and a near field transducer (NFT) with other write components of the head. Microwave assisted magnetic recording (MAMR) is also a recent development that improves the quality of written data by using a spin torque oscillator (STO) to apply a high frequency auxiliary magnetic field to the media close to the resonant frequency of the magnetic grains, thereby enabling the magnetic field generated by the write coil to more readily magnetize the disk surface.